Cancer, a genetic disorder caused by mutations of genes such as oncogene and tumor suppressor gene, is a serious life-threatening disease which is considered as top 1st or 2nd ranked leading cause of death in humans. Although various techniques have been developed for the treatment of cancer including surgical treatment, radiation therapy, immunotherapy, etc., problems related with inhibition and recurrence of malignant tumor still remain unresolved.
Protein kinase is a family of enzymes which plays an important role in signal transduction for various cellular activities including cellular proliferation, carcinogenesis, apoptosis, and cytodifferentiation, and it has been known that inhibitors thereof are useful in the treatment and prevention of proliferative diseases such as cancer (see Plowman, G. D, et al., Drug Discovery Today, 334-339 (1994)). In this regard, attempts have been made to treat proliferative diseases such as cancer by inhibiting protein kinase which is closely related with various signal transductions and disease mechanisms in cells.
IKKε and TBK1 are homologous Ser/Thr kinases which play an essential role in the innate immune responses derived by induction of Type I interferon and other cytokines, and are activated by viral and bacterial infection. The immune responses triggered by viral and bacterial infection include binding between Toll-like receptor and an antigen, e.g., lipopolysaccharide (LPS) or viral double-stranded RNA (dsRNA), followed by the activation of IKKε and/or TBK1 pathway. The activation of TBK1 and/or IKKε leads to phosphorylation of IFN regulatory factor 3 (IRF3) and/or IFN regulatory factor 7 (IRF7), which triggers dimerization and nuclear translocalization of interferon regulatory transcription factors, inducing signaling cascade that ultimately leads to the production of interferon (see Y.-H. Ou et al., Molecular Cell 41, 458-470, 2011 and D. A. Barbie et al., Nature, 1-5, 2009).
Recently, a study revealed that IKKε and TBK1 are over-activated in patients with colon cancer, breast cancer, brain tumor, gastric cancer, hepatic cancer, ovarian cancer, and the like (see J. S. Boehm et al., Cell 129, 1065-1079, 2007). Medications exhibiting inhibitory actions on IKKε and TBK1 block signal transduction pathways of IKKε and TBK1 by inhibiting phosphorylation of IRF3 and/or IRF7, which leads to the inhibition of angiogenesis, proliferation and survival of cancer, etc. Thus, it is expected that such medications can be effectively used as a therapeutic agent for treating cancer (see WO2010-100431 and WO2009-030890).
Additionally, it is known that IKKε and TBK1 play an important role not only in basic processes of memory and learning via cellular signaling pathways, but also in the regulation of learning ability and judgment (see Takaoka et al., Drug Delivery Rev 60, 847-857, 2008). It is also expected that IKKε and TBK1 inhibitors can be useful in the treatment and prevention of a wide range of diseases including inflammatory diseases as well as cancer.
Conventionally, a number of IKKε and TBK1 inhibitors have been developed, but such inhibitors have not yet been commercialized due to their poor effectiveness and deviations in therapeutic effects depending on the type of cancer. Thus, there is an increasing need for developing various compounds which are more effective in the treatment of cancer.